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<head>
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    <title>Document</title>
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<body>
    <script>
        /*赋值运算 +=，-=，*=，/=，%=
        前++，先自增，后运算
        后++，先运算，再自增*/
        var a = 10;
        var b = 20;
        // b+=a;
        // console.log(b);
        //b=b+a=30
        // b+=++a;
        b-=++a;
        a++;
        console.log(b);
        console.log(a);
        //b=b+a+1=31
        //b=b-(a+1)=9
        //a=a+1+1=12
    </script>
</body>
</html>